Continental Drift and Plate Tectonics

Alfred Wegener

● Some people thought the Earth was shrinking and cracking

● Wegener thought whole sections of the crust moved (plate tectonics)

● Some people did not understand and thought the continents floated around in the oceans (continental drift)

● He died before people accepted his ideas

Background to Continental Drifthttp://www.sciencechannel.com/tv-shows/greatest-discoveries/videos/100-greatest-discoveries-continental-drift/

Continental Drift

Continental Drift - Proof

Seafloor Spreading● Harry Hess figured out the mechanism that was moving the continents. This proved

Wegener’s theory. ● Surface of the earth is a thin layer of moving plates

Seafloor Spreading● Large continents begin to

crack and split apart ● The gaps fill with water ● Small seas become

oceans ● The mid ocean ridge

continues to produce new crust

J. Tuzo Wilson (1908 - 1993)

● A Canadian ● Developed theory of Plate tectonics

in the 1960s ● Used technology to further

Wegener’s ideas ● Plates of the Earth (20 in total) move

over a weak layer of hot rock very slowly

The Earth’s Plates

Earthquake epicentres

More Evidence - Magnetic Poles

More evidence has been found for Wegener’s theory

● The Earth’s North and South pole have flipped many times

● These leaves magnetic ‘stripes’ in rock containing iron minerals

So the Earth must be growing? ● Dense heavy oceanic crust can be

subducted (one plate moves under another) below less denser continental crust. ○ The friction melts rock

○ This magma rises through the crust to form

new volcanoes

● This is happening in South America (The Andes)

Recap - Seafloor spreading explainedhttp://nationalgeographic.org/encyclopedia/seafloor-spreading/

1. Valleys form due to natural circumstances, sometimes water can collect inside it. (picture 1 and 2)

2. As the continental crust continues to erode, a larger body of water can form over time and oceanic crust takes its place.

3. As the seafloor spreads, the ocean becomes larger. The oceanic crust continues to erode, cool, contract, and sink, new oceanic crust forms.

4. Eventually, the oceanic crust will split in two. The split pieces continue to spread away. In between the splits, you will find volcanoes/ocean mountain ridges.

Continents Collide ● Eventually when plates move

together the continental crust collides

● The heat and pressure make metamorphic rock

● It also pushes and folds the rocks into high mountains

● The Himalayas rise to 8848m and are still growing today

Convection Currents

Convection Currents ● Theory that plates are moved by an unequal distribution of heat● Convection – as fluid rises and carries heat with it, it is replaced with cooler

fluid which in turn rises again

Plate Tectonics

Plate Tectonic Processes

Plate Tectonic - Divergent

Plate Tectonics and Canada

Movement of Plates resulted in:

● Mountain ranges on east and west Coast ● Oil, gas, coal formed when Canada’s land mass in

warmer climates